Nowadays, polyester fiber is often applied not only to clothing, but also to general sheet materials for interiors because of the advantage that it is excellent in functionality, easiness of handling and fashionability. It is doubtless that such era in which polyester fiber is popular will continue more and its technical improvement and development will continue.
However, in recent years, in view of the global environmental conservation, enhancement of approaches to recycling and getting rid of petroleum-based synthetic fiber are strongly desired, and in the car industry which is a center of industry, there have been movements to take initiatives to solve this problem. In the fiber industry, too, it becomes essential to prepare for materials capable of converting to natural cultivation-reduction type.
In view of the above-mentioned background and looking toward the future, polylactic acid fiber or polytrimethylene terephthalate fiber is proposed and has been developed into practical use. Polytrimethylene terephthalate fiber has a low fiber Young's modulus and, in cases where it is used as a fabric such as a pile cloth, it forms a material having a very soft texture. In addition, it is understood to be a material excellent in light resistance and wear resistance.
As a fiber to be used for such a pile cloth, for example, 2 heater false twisting yarns of polytrimethylene terephthalate are proposed (i.e., refer to JP 2001-348740 A and Publication of JP Patent No. 3208362). However, in the 2 heater false twisting yarn of polytrimethylene terephthalate, crimp development by dry heat is large and results in a material having insufficient softness, and especially, a fabric with long piles having a high quality feeling cannot be obtained. In addition, its strength is insufficient and, for industrial material uses such as in cars where standards are high, it is a material which cannot satisfy such fabric standards.
As a material in which defects of polytrimethylene terephthalate material such as of the above-mentioned are improved and having handling properties of conventional polyester, a material in which polytrimethylene terephthalate and polyethylene terephthalate are composited into a core sheath configuration is proposed (i.e., refer to JP 2005-113279 A). However, since the softness of the material is lost in a later stage of processing, a further preferable false twisting yarn has been desired.
It could therefore be helpful to provide a false twisting yarn having a high strength and a soft texture when processed into a pile cloth, and capable of obtaining a pile cloth excellent in later stage processability.